Elaine K. Fukuda

A diffusion model for nonreactive ion loss in pulsed ion cyclotron resonance experiments

Abstract In a typical pulsed ion cyclotron resonance (ICR) experiment, gaseous ions formed by a pulsed electron beam are trapped by static electric and magnetic fields. The ions are trapped efficiently for several tenths of a second, but collisions with neutral molecules cause them to diffuse gradually to the walls of the analyzer cell. In this paper the diffusion of ions in an ICR trapped-ion analyzer cell is modeled theoretically, and the results are compared with experimental data obtained at a variety of pressures and trapping voltages. The theoretical model assumes that the dominant loss mechanism is diffusion of the ions to the upper and lower plates of the analyzer cell under the influence of an electrostatic trapping field. The theoretical results for the time dependence of the ion concentration in the ICR analyzer cell are in good agreement with experimental time plots. A useful parameter for characterizing ion trapping efficiency is t 1 2 , the time taken by the ion concentration to decrease to one-half of its initial value. The theoretical expression for t 1 2 shows that it is proportional to ( aB 2 )/ PV , where B is the magnetic field strength, a is the distance between the walls of the ICR analyzer cell, P is the pressure in the cell, and V is the electrostatic trapping voltage.

Electron affinities of SO2 and nitrobenzene

Several ion–molecule reactions have been observed which indicate that the electron affinities of SO2 and nitrobenzene are far greater than the currently accepted values. The reactions were studied by pulsed ion cyclotron resonance (ICR) spectrometry using a trapped ion analyzer cell to store the ions for several hundred ms. Reaction pathways were confirmed by ion cyclotron double resonance and by varying the pressures of the neutral reactants. The relative electron affinity of nitrobenzene and SO2 was determined by measuring the equilibrium constant for the reaction C6H5NO−2+SO2=SO2−+C6H5NO2, ΔG°=−3.0±0.2 kcal/mol. Pulsed ICR bracketing experiments support the following electron affinity values: E.A.(SO2)=2.2±0.1 eV and E.A.(C6H5NO2)=2.1±0.1 eV.

New insight into the mechanisms of reactions between some anionic nucleophiles and phenyl acetate in the gas phase

Abstract Experiments carried out in an ion cyclotron resonance (ICR) drif cell, an ICR trapped ion cell and a flowing afterglow (FA) system show that in the gas phase phenyl acetate reacts with a variety of clustered and unclustered nucleophiles to yield mainly the product ion C 6 H 5 O − .